Definition is absolutely the answer to what is most important for the quality of an image shot by a camera with an auto-focusing function, for example, a mobile phone. According to the a focusing method based on the principle of convex lens imaging, the relationship among focal length f, object distance u and image distance v is as follows:
            1      f        =                  1        u            +              1        v              ,that is, object distance u is inversely proportional to image distance after focal length f is fixed. On the other hand, according to the principle of motor focusing, if the focal length of a camera shot system is 4.88 mm, then image distance v is 4.885 mm when object distance u is 5 m but 5.130 mm when object distance u is 10 cm, that is, an image object difference of 0.245 mm is generated in the photographing of an object at a distance of 5 m and then an object at a distance of 10 m.
At present, the achievement of adjusting the camera shot to be far or near is through the locking of the lens of the camera in a voice coil motor, which is abbreviated as VCM. The VCM consists mainly of a coil, a magnet set and elastic sheets, and the coil is fixed in the magnet set by an upper and a lower elastic sheet. A magnetic field is generated by the coil when the coil is electrified, and the coil moves up under the interaction of the magnetic field of the coil with the magnet set, accompanied by the movement of the lens of the camera locked inside the coil. When powered off, the coil returns through the elastic force of the elastic sheets, thereby realizing an auto-focusing function.
A judgment on an auto-focusing motor of VCM elastic sheets is mainly according to the correspondence between current and object distance. In the correspondence between current and object distance, generally, a current of 15 mA is used as a starting current, that is, the minimal current. If each increase of the current by 10 mA results in the same driven distance, then the camera is qualified. If the precise is that each increase by 5 mA results in the same driven distance, then the camera is high-qualified, and so on. However, a corresponding error occurs if the correspondence between current and object distance is not a linear relation, and the images shot may be partially unclear, making it hard to provide a wholly clear image.
The above content is merely to assist in understanding the technical solution of the present document n but not for the acknowledging of the above content as the conventional art.